This section is intended to provide background information to facilitate a better understanding of the various aspects of the described embodiments. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.
Blowout preventers (“BOPs”) are used extensively throughout the oil and gas industry. Typical BOPs are used as a large specialized valve or similar mechanical device that seals, controls, and monitors oil and gas wells. The two most common types of BOPs are ram BOPs and annular BOPs, and these BOPs are often arranged in a BOP stack with at least one annular BOP stacked above several ram BOPs. The ram units in ram BOPs allow for shearing drill pipe with shear rams, sealing off around drill pipe with pipe rams, and sealing the BOP bore with blind rams. Typically, a BOP stack may be secured to a wellhead to provide a safe means for sealing the well in the event of a system malfunction.
An example ram BOP includes a main body or housing with a vertical bore. Ram bonnet assemblies may be bolted to opposing sides of the main body using a number of high tensile fasteners, such as bolts or studs. These fasteners hold the bonnet in position to enable the sealing arrangements to work effectively. An elastomeric sealing element may be used between the ram bonnet and the main body. There are several configurations, but essentially are all directed to preventing a leakage bypass between the mating faces of the ram bonnet and the main body.
Each bonnet assembly includes a piston that moves laterally within a ram cavity of the bonnet assembly by pressurized hydraulic fluid acting on the piston. The opposite side of each piston has a connecting rod attached thereto that in turn has a ram or ram assembly mounted thereon for extension into the vertical bore. The rams can be shear rams for shearing an object within the bore of a BOP or blind rams for sealing the BOP bore. Alternatively, the rams can be pipe rams for sealing off around an object within the bore of a BOP, such as a pipe, thereby sealing the annular space between the object and the BOP bore.
During normal operation, the BOPs may be subject to pressures up to 10,000 psi, or even higher. To accommodate such pressures, BOPs are becoming larger and stronger. For example, it is becoming increasingly common for BOP stacks and related devices to reach heights of about 30 feet or more and to be constructed from stronger or harder materials. However, these BOPs, even with all this supporting equipment, may still have difficulties cutting and shearing some tubular members though commonly used within the industry, and need to be constructed of a material that is NACE International compliant.